Conversion of various feeds to aromatic compounds is an industrially valuable process. Some conventional methods can allow for conversion of light alkanes. For example, a feed including light alkanes can be exposed to a combination of a dehydrogenation step and a cyclization/aromatization step to produce aromatics. Examples of such a process are described in U.S. Pat. Nos. 4,654,455 and 4,746,763. Unfortunately, the dehydrogenation process typically requires elevated temperatures while the cyclization/aromatization step prefers lower temperatures. As a result, the combination dehydrogenation and aromatization processes typically involve low conversion and extensive recycle, which increases the overall cost of producing the aromatics.
Other conventional methods for forming aromatics can include conversion of methanol and/or olefins to aromatics in the presence of a molecular sieve, such as ZSM-5. Reactions for conversion of methanol and/or olefins to aromatics can be useful, for example, for creation of aromatics as individual products, or for formation of aromatic and olefin mixtures for use as naphtha boiling range or distillate boiling range fuels.
U.S. Pat. Nos. 4,049,573 and 4,088,706 disclose that methanol can be converted to a hydrocarbon mixture rich in C2-C3 olefins and mononuclear aromatics, particularly p-xylene, by contacting the methanol at a temperature of 250-700° C. and a pressure of 0.2 to 30 atmospheres with a crystalline aluminosilicate zeolite catalyst which has a Constraint Index of 1-12 and which has been modified by the addition of an oxide of boron or magnesium either alone or in combination or in further combination with oxide of phosphorus. The above-identified disclosures are incorporated herein by reference.
Methanol can be converted to gasoline employing the MTG (methanol to gasoline) process. The MTG process is disclosed in the patent art, including, for example, U.S. Pat. Nos. 3,894,103; 3,894,104; 3,894,107; 4,035,430 and 4,058,576. U.S. Pat. No. 3,894,102 discloses the conversion of synthesis gas to gasoline. MTG processes provide a simple means of converting syngas to high-quality gasoline. The ZSM-5 catalyst used is highly selective to gasoline under methanol conversion conditions, and is not known to produce distillate range fuels, because the C10+ olefin precursors of the desired distillate are rapidly converted via hydrogen transfer to heavy polymethylaromatics and C4 to C8 isoparaffins under methanol conversion conditions.
One side reaction in conversion of methanol to gasoline is the formation of durene, which is a tetramethylated aromatic. Due to a unexpectedly high melting point, excess formation of durene can be less desirable during formation of gasoline. U.S. Pat. No. 4,476,338 describes one alternative for reducing or minimizing formation of durene during conversion of methanol to gasoline.
Olefinic feedstocks can also be used for producing C5+ gasoline, diesel fuel, etc. In addition to the basic work derived from ZSM-5 type zeolite catalysts, a number of discoveries contributed to the development of the industrial process known as Mobil Olefins to Gasoline/Distillate (“MOGD”). This process has significance as a safe, environmentally acceptable technique for utilizing feedstocks that contain lower olefins, especially C2 to C5 alkenes. In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givens disclose conversion of C2 to C5 olefins alone or in admixture with paraffinic components, into higher hydrocarbons over crystalline zeolites having controlled acidity. Garwood et al have also contributed improved processing techniques to the MOGD system, as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992. The above-identified disclosures are incorporated herein by reference.
Conversion of lower olefins, especially propene and butenes, over ZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as liquid fuels, especially the C5+ aliphatic and aromatic hydrocarbons. Olefinic gasoline is produced in good yield by the MOGD process and may be recovered as a product or recycled to the reactor system for further conversion to distillate-range products. Operating details for typical MOGD units are disclosed in U.S. Pat. Nos. 4,445,031, 4,456,779, Owen et al, and U.S. Pat. No. 4,433,185, Tabak, incorporated herein by reference.
In addition to their use as shape selective oligomerization catalysts, the medium pore ZSM-5 type catalysts are useful for converting methanol and other lower aliphatic alcohols or corresponding ethers to olefins. Particular interest has been directed to a catalytic process (MTO) for converting low cost methanol to valuable hydrocarbons rich in ethene and C3+ alkenes. Various processes are described in U.S. Pat. No. 3,894,107 (Batter et al), U.S. Pat. No. 3,928,483 (Chang et al), U.S. Pat. No. 4,025,571 (Lago), U.S. Pat. No. 4,423,274 (Daviduk et al) and U.S. Pat. No. 4,433,189 (Young), incorporated herein by reference. It is generally known that the MTO process can be optimized to produce a major fraction of C2 to C4 olefins. Prior process proposals have included a separation section to recover ethene and other gases from by-product water and C5+ hydrocarbon liquids. The oligomerization process conditions which favor the production of C10 to C20 and higher aliphatics tend to convert only a small portion of ethene as compared to C3+ olefins.
The methanol to olefin process (MTO) operates at high temperature and near 30 psig in order to obtain efficient conversion of the methanol to olefins. These process conditions, however, produce an undesirable amount of aromatics and C2 olefins and require a large investment in plant equipment.
The olefins to gasoline and distillate process (MOGD) operates at moderate temperatures and elevated pressures to produce olefinic gasoline and distillate products. When the conventional MTO process effluent is used as a feed to the MOGD process, the aromatic hydrocarbons produced in the MTO unit are desirably separated and a relatively large volume of MTO product effluent has to be cooled and treated to separate a C2− light gas stream, which is unreactive, except for ethene which is reactive to only a small degree, in the MOGD reactor, and the remaining hydrocarbon stream has to be pressurized to the substantially higher pressure used in the MOGD reactor.
Reverse flow reactors are well-suited for performing endothermic reactions that are facilitated by high temperature environments. U.S. Pat. No. 7,846,401 describes an example of a regenerative bed reverse flow reactor system, which is incorporated herein by reference. The reactor system is described as being suitable for a variety of pyrolysis reactions, such as hydropyrolysis of methane to form acetylene.
U.S. Pat. No. 6,372,949 describes methods for converting an oxygenate feed to gasoline or distillate boiling range compounds by exposing the oxygenate feed to a catalyst including a 10-member ring zeolite. The methods can optionally convert the oxygenate feed in the presence of a C4+ olefin co-feed which is described as improving the selectivity for formation of distillate boiling range compounds. An example of a suitable co-feed is described as a recycled cut of naphtha that is rich in heavy olefins, such as pentenes, hexenes, and heptenes. The Examples and Comparative Examples are directed to a comparison of conversion of a methanol feed relative to conversion of a feed containing 90 wt. % methanol and 10 wt. % hexene.
There is an ongoing desire to improve methods of converting methanol to aromatics that yield a higher amount of aromatics than prior art methods.